Electroforming as a method of creating lightweight, hollow jewelry, as well as other decorative and functional metal articles, is known in the art. Electroforming is a process in which a cast or mandrel is formed in the shape of the desired finished item. One or more thick metal layers is applied by electroplating. Then the mandrel is removed from the plated layer.
The following will describe prior art techniques for making electroformed jewelry and the shortcomings of those techniques. In the prior art, electroformed jewelry is typically composed of precious metals when the electroforming process is complete. In one prior art embodiment, the mandrel is formed of electrically conductive material, such as a white metal fusible alloy or solder. A copper layer is plated as a barrier to the molten white metal and to provide a bright finish. A thick layer of precious metal is then plated onto the mandrel. Typically, a copper protective layer is plated on top of the precious metal electroform to protect the gold or precious metal from splatter during the melt-out process. The mandrel is then melted or dissolved out through unplated apertures in the precious metal layer, leaving a hollow shell of precious metal. If the molten white metal were to contact the gold, unremovable stains and defects would be formed. However, such splattering is virtually unavoidable, even if great care is taken to prevent it. Only by subsequently replating the item can these defects be corrected. Also, the protective copper layer prevents formation of holes and cracks in the finished item caused by contact with high temperature tin. This problem occurs most frequently in items having complex shapes.
Subsequently, the protective copper layers are dissolved by using strong acids that do not affect the precious metal. Spent acids will contain the dissolved heavy metals which require treatment before disposal. Moreover, the precious metal layer must be substantially thick, and hence very expensive, to maintain the integrity of the hollow shell once the mandrel is melted out.
Attempts have been made to form costume jewelry having a much lower precious metal content by the electroforming process on white metal. However, the process used to form precious metal electroforms cannot be used to form costume jewelry. The strong acids used to dissolve the outer protective copper layer would attack the base metal electroform and destroy it.
The alternate prior art methods that have been developed employ wax mandrels instead of the fusible alloy mandrels. The typical method requires a wax mandrel to be formed, which is more complicated than casting a metal mandrel. The mandrel is sprayed with a conductive silver paint, which results in the loss of a substantial amount of silver. Then, the mandrel is laboriously affixed by hand to a plating rack by means of a pin pierced through the silver paint into the wax. The item is then electroplated with copper followed by the precious metal layer.
For electroformed precious metal jewelry, the precious metal layer is thick enough to maintain the integrity of the hollow shell once the core and electroplated copper are removed. In a special prior art method known as the "hollow shell" method, the wax core is removed after copper plating and prior to gold plating in order to prevent the stresses of expanding molten wax from cracking the gold. After wax removal, the hollow copper shell is gold electroformed. In both prior art precious jewelry methods, the copper is removed with strong acids leaving the gold shell. If the wax surface is sufficiently level and bright, and the gold deposit is ductile enough to withstand the expansion of the wax during melting, the copper layer can be omitted for precious jewelry electroforming.
In all cases, the wax mandrel is typically removed using solvents of high volatile organic content, which in turn requires the use of special solvent extraction equipment with the associated safety and environmental requirements. The copper is removed using strong acids, which have the drawbacks previously described.
These methods require skilled casting of the wax mandrel, application of a spray coat of highly conductive paints onto the wax mandrel, and labor intensive, time consuming, costly plating and processing. Such wax mandrels are also more fragile and deformable than the fusible alloy substrates used in precious metal electroforming. Additionally, to plate gold alloys of specific Karatage, computer controlled high speed plating systems must be used to produce finished goods of consistent quality.
Accordingly, a method is needed for making hollow articles of costume jewelry and the like based on a fusible metal alloy. Heretofore, a feasible method has not been disclosed. The prior art methods for making precious hollow jewelry using white metal mandrels involve a complicated procedure generating substantial volumes of toxic waste. The method described herein is environmentally friendlier and simpler for high volume manufacturing.